Key Chain Tracer (KCT) a RJ-45 plug with 3VDC button cell on Pin-1 (+) & Pin-2 (-)
Attach RJ-45 plug to CR1632/2032/2016 by stripping leads, coil and bond using heat shrink.
KCT used to check OSI-1 FO link from device / media converters Tx circuit.
Dipswitch defeat Link Pass Thru and Far End Fault to transmit continuously for troubleshooting.
if KCT is on key ring, you will have it when you need it, and not leave work without it.
Use cell phone camera to see the IR light emitted from LED/FO. Plug in KCT to MC:
IF MC Tx lights: MC works; might be device or FO link, check far end of fiber
IF MC Tx no light: MC bad

DISCLAIMER: USE AT OWN RISK
3VDC across leads in MC shouldn't hurt it. Typical Ethernet is ±2.5VDC (5V delta)
Most media converter that are POE compatible are more robust with tolerances
This device will NOT help you find your keys, it is a TRACER not a TRACKER;
unless you notice a device that is still off-line, with your keys plugged into it